firebird446

I have a 4l60e raptor stage 3 with a 2300-2500 stall and car does great while accel thru gears up until 90 mph and starts vibrating hum noise. Really loud when I let off and it shift into 4th and won't quit until I get to a lower speed around 70-75. Car will still pull like crazy thru vibration. I have a pollyurathane trans mount for awhile now. I'm just wondering if its the u-joints/driveahaft.

ArkBird96

Those poly trans mounts are known to transmit A LOT of vibration to the cabin of the car. I would start there. I would be willing to bet that the poly mount is the source of your vibration.